12/01/2026
Spinal Muscular Atrophy (SMA) - Carrier Screening and Newborn Screening in the UK.
What is SMA?
Spinal Muscular Atrophy (SMA) is a genetic neuromuscular condition that affects the motor neurones that control voluntary muscle movement. Loss of these neurones leads to progressive muscle weakness and muscle wasting. Intelligence, learning ability and sensation are not affected.
Cause and Genetics
SMA is caused by absence or malfunction of the SMN1 gene. Both copies of the gene must be affected for SMA to develop. A related gene, SMN2, produces small amounts of the same protein and modifies severity, but does not precisely predict outcome.
Inheritance
SMA is inherited in an autosomal recessive pattern. Parents are usually healthy carriers. If both parents are carriers, each pregnancy has a 25% chance of being affected.
How common is SMA?
Approximately 1 in 10,000 babies are born with SMA. Around 1 in 40–60 people are carriers.
Types of SMA
Type
Typical onset
Motor abilities (historical)
Type 0
Before birth
Severe weakness, respiratory failure at birth
Type 1
< 6 months
Unable to sit independently
Type 2
6–18 months
Can sit but not walk
Type 3
Childhood
Walks initially, later weakness
Type 4
Adulthood
Mild, slowly progressive weakness
UK-Specific Clarification
Spinal Muscular Atrophy (SMA) is not included in the UK NHS newborn blood spot (heel-prick) screening programme.
Newborn Screening (NHS-aligned)
Newborn screening aims to identify babies who are very likely to have SMA so they can be referred promptly for specialist assessment and early treatment. A positive screening result is not a diagnosis and does not predict severity. Confirmatory genetic testing is always required.
Carrier Screening (NHS GEP-aligned)
Carrier screening identifies individuals who carry one non-working copy of the SMN1 gene. Carriers are healthy and do not develop SMA. If both partners are carriers, there is a 1 in 4 chance in each pregnancy that the baby will be affected. A negative result significantly reduces, but does not eliminate, the chance of being a carrier.
The Natera Horizon carrier screen blood test screens for a wide range of recessive conditions like SMA.
https://innermosthealthcare.com/product/natera-horizon-carrier-screen/
If a woman is screen negative her babies wont get SMA. If she carries the gene then her partner can have the test with no lab fee. If he is is screen negative her babies wont get SMA. If he is a carrier too then there is a 1:4 chance of an affected baby and she can have prenatal testing by amniocentesis or ensure baby has early newborn screening.
https://innermosthealthcare.com/product/fulgent-newborn-screening-test/
Treatment and Support
SMA is now a treatable condition. Disease-modifying treatments increase SMN protein levels and are most effective when started early, ideally before symptoms develop. Supportive care includes respiratory, nutritional, physiotherapy, occupational therapy and orthopaedic management.
Further Information
Being given information about Spinal Muscular Atrophy (SMA) can feel overwhelming. Reliable information and specialist support are available.
NHS Support
NHS Newborn Blood Spot Screening Programme
Provides information about newborn screening, including SMA, and what screening results mean.
• Information for parents about the heel-prick test
• Explanation of screening results and follow-up pathways
• NHS-approved patient resources
Parents can also speak to their midwife, health visitor, GP, or specialist team for personalised advice and support.
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UK National Screening Committee (UK NSC)
The UK NSC advises governments across the UK on which conditions should be included in national screening programmes.
• Reviews evidence on benefits and risks of screening
• Provides reassurance that screening decisions are evidence-based
• Oversees national policy on newborn screening
UK NSC recommendations underpin the inclusion of SMA in newborn screening in England.
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SMA UK (Patient Support Organisation)
SMA UK is the main UK charity supporting people affected by SMA and their families.
They provide:
• Clear, trustworthy information about SMA
• Emotional and practical support for families
• Access to specialist nurses and advisors
• Information about living with SMA, education, and equipment
• Opportunities to connect with other families
Many families find it helpful to speak to others who have experience of SMA alongside receiving medical care.
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Genetic Counselling and Specialist Care
Families affected by SMA, or identified as carriers, are usually offered access to:
• Clinical genetics services
• Genetic counselling, to explain results and options
• Specialist paediatric neuromuscular teams, coordinated through the NHS
These services aim to support informed decision-making and ongoing care.
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Important Reassurance
• SMA is no one’s fault
• Parents are usually healthy carriers without knowing
• SMA is now a treatable condition
• Early diagnosis allows the best possible outcomes
• Support is available at every stage
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Leaflet Disclaimer
This leaflet is intended to provide general information and support.
It does not replace discussions with your healthcare professionals, who can give advice tailored to your individual circumstances.
Innermost Healthcare | Ashtree Medical Clinic, Cardiff
HIW Registered Clinic | Prepared by Dr Bryan Beattie MD FRCOG, Consultant in Fetal Medicine